1. Field of the Invention
The present invention relates to a scanning exposure apparatus and a method of manufacturing a device.
2. Description of the Related Art
A reduction projection exposure apparatus has conventionally been employed in a process of manufacturing semiconductor devices such as an LSI and VLSI formed from ultrafine patterns. This apparatus reduces a circuit pattern drawn on a mask (reticle) and projects and prints it by exposure on a substrate (wafer) coated with a photosensitive agent, thereby forming a desired pattern on the substrate.
Along with an improvement in the packaging density of semiconductor devices, further advance of micropatterning is required. This demand is increasing even for the exposure apparatus along with the development of the resist process.
To improve the resolution of the exposure apparatus, there are a method of shortening the exposure wavelength and a method of increasing the numerical aperture (NA) of the reduction projection optical system. As the resolution improves, the depth of focus of the reduction projection optical system decreases. Therefore, it is an important issue to attain both an improvement in resolution and the assurance of the depth of focus necessary for the process involved.
Japanese Patent No. 2576798 discloses a technique of attaining both an improvement in resolution and the assurance of the depth of focus by synchronizing a change in the central wavelength of the exposure light and the pulsed oscillation of the exposure light using the chromatic aberration of the projection optical system, and integrating images formed at different positions.
However, the scanning exposure apparatus adjusts the exposure amount integrated within the scanning time to be constant against nonuniformity of the illumination light by changing the width of the aperture and the light intensity in the aperture in a direction perpendicular to the scanning exposure direction. In this case, the light intensity in the aperture in a direction perpendicular to the scanning direction is often nonuniform.
Even when the technique disclosed in Japanese Patent No. 2576798 is applied to a scanning exposure apparatus which generates a nonuniform light intensity distribution in the slit aperture in a direction perpendicular to the scanning exposure direction, a wavelength vs. intensity distribution obtained by integrating the intensity by changing the central wavelength of the exposure light changes depending on the position in the aperture. The variation in wavelength vs. integrated intensity distribution is a difference in integrated focus distribution, which causes a variation in best imaging position depending on the position in the aperture and the scanning exposure integration position. This often results in a decrease in the depth of focus common in the entire scanning exposure field.